Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs. This is increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease.
In certain types of medication delivery devices, such as pen type devices, cartridges of medication are used. These cartridges are housed in a cartridge holder or cartridge housing. Such cartridges include a bung or stopper at one end. At the other end of the cartridge, the cartridge comprises a pierceable seal. To dispense a dose of medication from such a cartridge, the medication delivery device has a dose setting mechanism that uses a spindle to move in a distal direction towards the cartridge and to press a distal end of the spindle against the bung. This expels a certain set dose of medication from the cartridge. It is therefore important that the distal end of the spindle does not press on the bung except during normal dose dispense, otherwise some loss of drug may be experienced and the subsequent dose would be below the set value.
One perceived disadvantage of certain known medication delivery devices is that because of the various tolerance differences that may occur during manufacturing (e.g., tolerance differences that may arise during component molding) of the various parts making up the drug delivery device, the combination of these various tolerance differences result in that the cartridge may or may not be held rigidly within the cartridge holder. In other words, the cartridge (and hence cartridge bung) may move away relative to the distal end of the spindle. Therefore, there may be times where the cartridge is not held rigidly within the cartridge holder and can therefore move away from an inner front surface of the cartridge holder.
In addition, a needle assembly must frequently be attached to and removed from the cartridge holder. This allows a double ended needle of the needle assembly to pierce the seal of the cartridge. Frequently attaching and re-attaching needle assemblies may cause the cartridge to move within the cartridge holder.
One advantage of certain typical pen type drug delivery devices is that they are relatively compact. This allows a user to carry around the pen. However, if a user of such pen type delivery devices were to drop or mishandle the device, again movement of the cartridge away from the most distal portion of the cartridge holder could result.
There is, therefore, a general need to take these various perceived issues into consideration when designing either resettable or non-resettable pen type drug delivery devices. Such drug delivery devices would help to prevent unwanted movement of a cartridge contained within a cartridge holder. Specifically, such drug delivery devices would help prevent the cartridge from moving axially relative to the cartridge holder during use of the pen type delivery device: when a needle assembly is attached or removed, or when a user carries around (or drops the drug delivery device) during normal use. Preventing such unwanted movement of the cartridge within the cartridge holder would tend to help insure dispensing accuracy by the device by preventing the spindle distal end from pressing on the bung of the cartridge.